Optical surface identification for laser surgery

Abstract

Systems and methods automatically locate optical surfaces of an eye and automatically generate surface models of the optical surfaces. A method includes OCT scanning of an eye. Returning portions of a sample beam are processed to locate a point on the optical surface and first locations on the optical surface within a first radial distance of the point. A first surface model of the optical surface is generated based on the location of the point and the first locations. Returning portions of the sample beam are processed so as to detect second locations on the optical surface beyond the first radial distance and within a second radial distance from the point. A second surface model of the optical surface is generated based on the location of the point on the optical surface and the first and second locations on the optical surface.

What is claimed is: 
     
       1. A method of identifying optical surfaces in an eye for performing laser surgery on the eye, the eye including a cornea having anterior and posterior surfaces, a lens capsule having anterior and posterior surfaces, an iris, and a limbus, the method comprising:
 coupling the eye to a laser eye surgery system that includes an optical coherence tomography (OCT) imaging subsystem, the OCT imaging subsystem including a reference path length that is adjustable so that a distance from the laser eye surgery system to a detection window of the OCT imaging subsystem is adjustable, the OCT imaging subsystem employing a detection beam having a plurality of wavelengths such that the detection window spans a range of distances relative to the laser eye surgery system; 
 generating an OCT sample beam; 
 focusing the OCT sample beam at a plurality of different locations within the eye, the plurality of different locations include at least two different distances from the laser eye surgery system, the different distances defining a depth range encompassing an expected variability of distance from the laser eye surgery system to the corneal anterior surface, to the lens capsule anterior surface, or the lens capsule posterior surface; and 
 processing returning portions of the sample beam focused at the plurality of different locations to locate, relative to the laser eye surgery system, the corneal anterior surface, the lens capsule anterior surface, or the lens capsule posterior surface. 
 
     
     
       2. The method of  claim 1 , wherein the different locations are positioned at least three different distances from the laser eye surgery system. 
     
     
       3. The method of  claim 2 , wherein the different locations are located at least four different distances from the laser eye surgery system. 
     
     
       4. The method of  claim 3 , wherein:
 the different locations are positioned at least five different distances from the laser eye surgery system; and 
 the five different distances define four intervening separating distances of between 0.25 mm and 0.75 mm. 
 
     
     
       5. The method of  claim 4 , wherein at least one of the four intervening separating distances is between 0.4 mm and 0.6 mm. 
     
     
       6. The method of  claim 1 , wherein said focusing the OCT sample beam at a plurality of different locations within the eye includes scanning the OCT sample beam in a pattern having a maximum transverse dimension of less than 2.0 mm for at least two of the different distances. 
     
     
       7. The method of  claim 6 , wherein the pattern has a maximum transverse dimension of less than 1.2 mm for at least two of the different distances. 
     
     
       8. The method of  claim 1 , wherein the reference path length is held constant during said focusing the OCT sample beam at a plurality of different locations within the eye. 
     
     
       9. The method of  claim 1 , wherein a boundary surface within the detection window divides the detection window into a real portion of the detection window and an imaginary portion of the detection window, the detection window imaginary portion being disposed between the laser eye surgery system and the detection window real portion. 
     
     
       10. The method of  claim 9 , wherein the laser eye surgery system is configured to employ an interface lens assembly that is removably mounted to the laser eye surgery system so as to be disposed between the OCT imaging subsystem and the eye, the interface lens assembly including an interface lens having an anterior surface and a posterior surface, the method further comprising:
 setting the reference path length to position the detection window boundary surface between the interface lens posterior surface and the corneal anterior surface such that the interface lens posterior surface is closer to the detection window boundary surface than the corneal anterior surface when processing returning portions of the sample beam focused at the plurality of different locations to locate the corneal anterior surface. 
 
     
     
       11. The method of  claim 9 , wherein the laser eye surgery system is configured to employ an interface lens assembly that is removably mounted to the laser eye surgery system so as to be disposed between the OCT imaging subsystem and the eye, the interface lens assembly including an interface lens having an anterior surface and a posterior surface, the method further comprising:
 setting the reference path length to position the detection window boundary surface between the interface lens posterior surface and the lens capsule anterior surface such that the interface lens posterior surface is further from the detection window boundary surface than the lens capsule anterior surface when processing returning portions of the sample beam focused at the plurality of different locations to locate the lens capsule anterior surface. 
 
     
     
       12. The method of  claim 11 , wherein the detection window boundary surface is positioned such that the cornea anterior surface is closer to the detection window boundary surface than the lens capsule anterior surface when processing returning portions of the sample beam focused at the plurality of different locations to locate the lens capsule anterior surface. 
     
     
       13. The method of  claim 9 , further comprising setting the reference path length to position the lens capsule posterior surface between the detection window boundary surface and the lens capsule anterior surface when processing returning portions of the sample beam focused at the plurality of different locations to locate the lens capsule posterior surface. 
     
     
       14. The method of  claim 1 , wherein the laser eye surgery system is configured to employ an interface lens assembly that is removably mounted to the laser eye surgery system so as to be disposed between the OCT imaging subsystem and the eye, the interface lens assembly including an interface lens having an anterior surface and a posterior surface, the method further comprising using the OCT imaging system to locate the interface lens posterior surface. 
     
     
       15. The method of  claim 14 , further comprising using the OCT imaging system to locate the interface lens anterior surface. 
     
     
       16. The method of  claim 1 , wherein the laser eye surgery system is configured to employ an interface assembly that is removably mounted to the laser eye surgery system so as to be disposed between the OCT imaging subsystem and the eye, the interface assembly including two or more reference features, the method further comprising:
 using the OCT imaging subsystem to locate the reference features relative to the laser eye surgery system; and 
 comparing the OCT based locations of the reference features relative to predetermined positions of the reference features to determine at least one of that the interface assembly is properly mounted to the laser eye surgery system, that the interface assembly is improperly mounted to the laser eye surgery system, that fluid is present in the interface assembly, that fluid is missing from the interface assembly, an angular orientation of the interface assembly relative to the laser eye surgery system, or whether the interface assembly is coupled with a left or a right eye of a patient. 
 
     
     
       17. The method of  claim 16 , wherein the interface assembly comprises:
 a suction ring assembly that is configured to be coupled with the eye and includes the two or more reference features; and 
 an interface lens assembly that includes an interface lens and couples the suction ring assembly to the laser eye surgery system. 
 
     
     
       18. A method for processing optical coherence tomography (OCT) data to generate a surface model of an optical surface of an eye, the eye including a cornea having anterior and posterior surfaces, a lens capsule having anterior and posterior surfaces, an iris, and a limbus, the method comprising:
 coupling the eye to a laser eye surgery system that includes optical coherence tomography (OCT) imaging subsystem, the OCT imaging subsystem including a reference path length that is adjustable so that a distance from the laser eye surgery system to a detection window of the OCT imaging subsystem is adjustable, the OCT imaging subsystem employing a detection beam having a plurality of wavelengths such that the detection window spans a range of distances relative to the laser eye surgery system; 
 generating an OCT sample beam; 
 processing returning portions of the sample beam to locate a point on the optical surface relative to the laser eye surgery system; 
 focusing the OCT sample beam within the eye with the length of the reference path set to position the detection window based on the location of the point on the optical surface such that the detection window encompasses the optical surface for all expected variations in spatial disposition of the optical surface; 
 processing returning portions of the sample beam so as to detect first locations on the optical surface within a first radial distance of the point on the optical surface; 
 generating a first surface model of the optical surface based on the location of the point on the optical surface and the first locations on the optical surface; 
 processing returning portions of the sample beam so as to detect second locations on the optical surface beyond the first radial distance and within a second radial distance from the point on the optical surface; and 
 generating a second surface model of the optical surface based on the location of the point on the optical surface and the first and second locations on the optical surface. 
 
     
     
       19. The method of  claim 18 , wherein the optical surface is the cornea anterior surface, the lens capsule anterior surface, or the lens capsule posterior surface. 
     
     
       20. The method of  claim 19 , further comprising:
 processing returning portions of the sample beam so as to detect third locations on the optical surface beyond the second radial distance and within a third radial distance from the point on the optical surface; and 
 generating a third surface model of the optical surface based on the location of the point on the optical surface and the first, second, and third locations on the optical surface. 
 
     
     
       21. The method of  claim 20 , wherein said processing returning portions of the sample beam so as to detect third locations comprises generating a second search volume defined by a second upper limit surface and a second lower limit surface, the second upper and lower limit surfaces being offset from the second surface model on respective opposing sides of the second surface model, and wherein said processing returning portions of the sample beam focused at the plurality of different locations so as to detect third locations is limited to the second search volume. 
     
     
       22. The method of  claim 18 , wherein said processing returning portions of the sample beam so as to detect second locations comprises generating a search volume defined by a first upper limit surface and a first lower limit surface, the first upper and lower limit surfaces being offset from the first surface model on respective opposing sides of the first surface model, and wherein said processing returning portions of the sample beam focused at the plurality of different locations so as to detect second locations is limited to the search volume. 
     
     
       23. The method of  claim 18 , further comprising:
 processing returning portions of the sample beam so as to detect third locations on the optical surface beyond the second radial distance and within a third radial distance from the point on the optical surface; and 
 generating a third surface model of the optical surface based on the location of the point on the optical surface and the first, second, and third locations on the optical surface. 
 
     
     
       24. The method of  claim 18 , wherein at least one of the first and second surface models is an ellipsoid surface model, a spherical surface model, or a conicoid surface model. 
     
     
       25. The method of  claim 18 , wherein a boundary surface within the detection window divides the detection window into a real portion of the detection window and an imaginary portion of the detection window, the detection window imaginary portion being disposed between the laser eye surgery system and the detection window real portion. 
     
     
       26. The method of  claim 25 , wherein:
 the optical surface is the lens capsule anterior surface; and 
 the reference path length is set to position the lens capsule anterior surface between the detection window boundary surface and the laser eye surgery system. 
 
     
     
       27. The method of  claim 25 , wherein:
 the optical surface is the lens capsule posterior surface; and 
 the reference path length is set to position the lens capsule posterior surface between the detection window boundary surface and the laser eye surgery system. 
 
     
     
       28. The method of  claim 18 , comprising:
 calculating a transverse distance between an apex of the optical surface and a central axis of the laser eye surgery system; 
 comparing the calculated transverse distance to a predetermined acceptable transverse distance value; and 
 inhibiting treatment of the eye if the calculated transverse distance exceeds the predetermined acceptable transverse distance value. 
 
     
     
       29. A method of identifying optical surfaces in an eye for performing laser surgery on the eye, the eye including a cornea having anterior and posterior surfaces, a lens capsule having anterior and posterior surfaces, an iris, a pupil, and a limbus, the method comprising:
 coupling the eye to a laser eye surgery system that includes an optical coherence tomography (OCT) imaging subsystem, the OCT imaging subsystem including a reference path length that is adjustable so that a distance from the laser eye surgery system to a detection window of the OCT imaging subsystem is adjustable, the OCT imaging subsystem employing a detection beam having a plurality of wavelengths such that the detection window spans a range of distances relative to the laser eye surgery system; 
 using the OCT imaging subsystem to locate a centrally-located point on the lens capsule anterior surface; 
 directing an OCT sample beam into the eye with the reference path length set to position the detection window to encompass the lens capsule anterior surface and the iris; 
 processing returning portions of the sample beam to identify, relative to the laser eye surgery system, a plurality of edge points within the detection window, each edge point being disposed on an optical surface; 
 generating a surface model of the lens capsule anterior surface based on the location of the centrally-located point on the lens capsule anterior surface and a subset of the edge points; 
 selecting a subset of the edge points that are offset from the surface model of the lens capsule anterior surface; and 
 generating a surface model of the iris based on the subset of the edge points that are offset from the surface model of the lens capsule anterior surface. 
 
     
     
       30. The method of  claim 29 , wherein the surface model of the iris is an oriented plane. 
     
     
       31. The method of  claim 29 , further comprising:
 using the OCT imaging subsystem to generate a surface model of the cornea anterior surface; 
 generating a curved-line intersection between the iris surface model and the cornea anterior surface model; and 
 using the curved-line intersection to represent the location of the limbus. 
 
     
     
       32. The method of  claim 29 , further comprising processing a video image of the eye to identify the pupil by searching outwardly from a central location to identify edges of the iris. 
     
     
       33. The method of  claim 32 , further comprising generating a curved-line model of the pupil based on the video identified pupil and the iris surface model. 
     
     
       34. A method of generating a surface model of a posterior surface of a cornea of an eye, the cornea having an anterior surface, the method comprising:
 coupling the eye to a laser eye surgery system that includes an optical coherence tomography (OCT) imaging subsystem, the OCT imaging subsystem including a reference path length that is adjustable so that a distance from the laser eye surgery system to a detection window of the OCT imaging subsystem is adjustable, the OCT imaging subsystem employing a detection beam having a plurality of wavelengths such that the detection window spans a range of distances relative to the laser eye surgery system; 
 directing an OCT sample beam into the eye with the reference path length set to position the detection window to encompass the cornea; 
 generating a search volume defined by a first upper limit surface and a first lower limit surface, the first upper and lower limit surfaces being offset from a surface model of the cornea anterior surface; and 
 processing returning portions of the OCT sample beam corresponding to the search volume to identify points located on the cornea posterior surface. 
 
     
     
       35. The method of  claim 34 , wherein at least one of the first upper and lower limit surfaces is a sphere, an ellipsoid, or a conicoid. 
     
     
       36. A system for identifying optical surfaces in an eye for performing laser surgery on the eye, the eye including a cornea having anterior and posterior surfaces, a lens capsule having anterior and posterior surfaces, an iris, and a limbus, the system comprising:
 a laser eye surgery system; 
 an OCT imaging subsystem, the OCT imaging subsystem including a reference path length that is adjustable so that a distance from the laser eye surgery system to a detection window of the OCT imaging subsystem is adjustable, the OCT imaging subsystem employing a detection beam having a plurality of wavelengths such that the detection window spans a range of distances relative to the laser eye surgery system; and 
 a processor coupled to the laser eye surgery system and the OCT imaging subsystem, the processor configured to interact with the laser eye surgery system and the OCT imaging subsystem.